Constant and high switching frequency torque controller for DTC drives

The letter presents a new method of increasing the switching frequency of a direct torque control (DTC) of induction machines. The method simply replaces the hysteresis comparator of the conventional DTC drives with a triangular waveform-based constant switching frequency controller. By synchronizing the digital signal processor (DSP) sampling with a triangular waveform and with an appropriate systematic controller design, a high switching frequency DTC drive is possible without requiring a high-frequency space-vector modulator. The implementation of the controller is simple and operates based on waveform comparisons; in this letter it is implemented using a combination of a DSP and a field programmable gate array device. Simulation and experimental results indicate that the controller both reduces the torque ripple and maintains a constant switching frequency.     

Synthesis of the Orthorhombic Phase of ZrO2

Single-phase orthorhombic ZrO₂ was prepared by quenching from high temperature and high pressure. The lattice parameters are a₀=0.5042, b₀=0.5092, and c₀=0.5257 nm; the calculated density is 6.09 Mg·m⁻³. This phase is metastable under atmospheric pressure and reverts to the monoclinic phase either on heating above 300°C or when it is ground in a mortar.     

Large-Scale Shake Table Experiment and Numerical Simulation on the Nonlinear Behavior of Pile-Groups Subjected to Large-Scale Earthquakes

This paper describes the results of large-scale shake-table experiments involving a 3×3 pile-group. The pile-group was embedded in dry sand and subjected to sinusoidal waves and an earthquake motion recorded from the 1995 Hyogo-ken Nanbu (Kobe) earthquake. The load transfer between soil and pile was derived and the group effect was captured. Numerical simulations were also performed using a Beam-on-Nonlinear-Winkler-Foundation approach with a new hysteretic p-y curve. A comparison of the experimental and numerical results revealed that the numerical simulation is capable of accounting for the soil-pile interaction observed in the experiment.     

Mobile multicasting in wireless ATM networks

Multicasting is a desired function in both wired and wireless networks. Currently, multicasting‐based applications have pervasive presence and influence in our Internet. Wireless ATM aims to support different traffic types over a high speed wireless network. In particular, traditional approaches towards multicasting in wired networks cannot be directly applied to mobile ATM networks. This includes the mechanism proposed to handle mobility in wired networks. In this paper, we address the issues behind multicasting in wireless ATM networks and the underlying mechanisms to support handoffs of both unicast and multicast connections. Through simulation, we evaluated the performance of optimal core‐based tree (CBT), late‐joined CBT, optimal source‐based tree (SBT), and late‐joined SBT during changing multicast host membership conditions. In addition, we evaluated the impact of multicast receivers' migration on the total link cost of the resultant multicast tree. Simulation results revealed that source‐based trees incur more total link costs under both dynamic host membership and receivers' migration scenarios. However, it generates less control messages than the distributed CBT and SBT approaches. This revised version was published online in June 2006 with corrections to the Cover Date.     

Instability of plastic flow in mild steel

Plastic flow localization in the yielding of mild steel is theoretically studied in terms of the instability of the uniform mode of yielding. The instability is judged by the small perturbation theory in which the development of non-uniform modes superimposed upon the basic uniform mode is examined. The constitutive equation of rate-dependent type and the criterion of yield initiation at the plastic-zone front are employed as the constitutive relations of mild steel. The results of the analysis show the relation between the instability and the characteristic nature of mild steel.     

Effects of compressive strain on the evolution of interfacial strength of steel/nickel solid-state bonding at low temperature

Solid-state bonding between ultralow-carbon steel and pure nickel was conducted by hot pressing with various compressive strain ranging from 5 to 15% and subsequent isothermal holding at 923?K. It was found that the interfacial strength of contact area is accounted for by the evolution of the intrinsic strength of the interface and the amount of plastic energy dissipation at the crack tip during interface fracture. The compression induces severe deformation around the interface and consequently inhibits the plastic energy dissipation during interface fracture. In the first stage of isothermal holding, the residual strain around the interface on the steel side is reduced by recovery process, which concurrently decreases in the yield stress of the area adjacent to the interface. This promotes plastic energy dissipation of the area, leading to a significant increase in interfacial strength in the first stage.     

Effect of simultaneous surface modification process on wear resistance of martensitic stainless steel

In order to improve the wear resistance of martensitic stainless steel, a surface treatment system was developed that combines high-frequency induction heating (IH) with fine particle peening (FPP). In this system, a compressed air spray from the FPP nozzle rapidly cools the specimen surface, which is heated by the IH system. The specimen surface can be simultaneously modified by work hardening and quenching. Vickers hardness and retained austenite measurements were conducted to characterize the surface-modified layer generated by the developed process. Surface microstructures were also observed by scanning electron microscopy (SEM) and optical microscopy. The process created a surface with a high hardness and an extremely fine-grained microstructure. The fine-grained microstructure was generated by dynamic recrystallization. The process reduced the amount of retained austenite in the surface layer because it increased the precipitated chromium carbide content. Reciprocating sliding wear tests were conducted to evaluate the wear resistance of the surface. The specimen modified by the developed process exhibited higher wear resistance than specimens that had only been quenched. This implies that the developed simultaneous process can significantly improve the wear resistance of steel surfaces.     

Fundamental welding R&D results for manufacturing vacuum vessel of JT-60SA

The real vacuum vessel (VV) manufacturing of JT-60SA has started since November 2009 at Toshiba. Prior to starting manufacturing, fundamental welding R&Ds had been performed by three stages. In the first stage, primary tests for screening welding method were performed. In the second stage, the trial welding for 1 m-long straight and curved double shell samples were conducted. The dependences of welding quality and distortion on the welding conditions, such as arc voltage and current, setting accuracy, welding sequence, and the shape of grooves were studied. In addition, welding condition with low heat input was explored. In the last stage, fabrication sequence was confirmed and established by the trial manufacturing of the 20° upper half mock-up [1]. This paper presents the R&D results obtained in the first and second stages.